1. Field of the Invention
The present invention relates to an exhaust gas cleaning system for internal combustion engines, adapted to supply secondary air uniformly to the exhaust ports of cylinders of the engine to effectively oxidize and remove unburnt noxious components in the exhaust gas.
2. Description of the Prior Art
Such an exhaust gas cleaning system for multi-cylinder internal combustion engines has been known as having secondary air supply passages leading to the exhaust ports of cylinders and a reed valve device disposed in the secondary air supply system. The reed valve device is adapted to be opened by the pulsation of the exhaust gas pressure to permit the introduction of the secondary air to the exhaust ports.
This known system, however, has the following disadvantages. Namely, the supply of the secondary air to the exhaust ports is made non-uniformly or, in the worst case, some of the exhaust ports cannot receive sufficient secondary air, because of differences in the flow resistance in the secondary air passages due to differences in length and diameter of the passages, as well as mutual interference of the pulsating exhaust pressures between the exhaust ports. This problem becomes serious particularly when the number of the cylinders is increased.